[CP2K-user] Spikes in GAPW total electron density cube

[Mayank Dodia]

Hi all,

I am trying to extract total electron density from a cluster of water 
molecules in a QM/MM calculation and I am using 6-31G* all electron basis 
to extract the total electron density cube of the water molecules in the QM 
region. As you can see in the attached image, the electron density shows 
"spikes". The description of the TOTAL_DENSITY keyword does gives the 
warning, which says that:

"..NOTE: The total density in real space might exhibit unphysical features 
like spikes due to the finite and thus truncated g vector expansion."

My question here is that is there any way by which I can reduce the 
prevalence of spikes in the total electron density by fine tuning GAPW 
parameters? I am currently using the following setup:

     &QS
       EPS_DEFAULT     1.0000000000000000E-10
       EPSFIT     9.9999999999999995E-07
       EPSISO     9.9999999999999998E-13
       EPSRHO0     1.0000000000000000E-08
       ALPHA0_HARD     1.0000000000000000E+01
       MAP_CONSISTENT  T
       LMAXN1  6
       LMAXN0  4
       QUADRATURE  GC_LOG
       EXTRAPOLATION  ASPC
       EXTRAPOLATION_ORDER  4
       METHOD  GAPW
     &END QS
     &MGRID
       CUTOFF     2.8000000000000000E+02
       COMMENSURATE  T
     &END MGRID
     &XC
       DENSITY_CUTOFF     1.0000000000000000E-10
       GRADIENT_CUTOFF     1.0000000000000000E-10
       TAU_CUTOFF     1.0000000000000000E-10
       &XC_GRID
         XC_SMOOTH_RHO  NN50
         XC_DERIV  SPLINE2_SMOOTH
       &END XC_GRID
       &XC_FUNCTIONAL  NO_SHORTCUT
         &PBE  T
           PARAMETRIZATION  REVPBE
         &END PBE
       &END XC_FUNCTIONAL
       &VDW_POTENTIAL
         POTENTIAL_TYPE  PAIR_POTENTIAL
         &PAIR_POTENTIAL
           R_CUTOFF     1.2500000000000009E+01
           TYPE  DFTD3
           PARAMETER_FILE_NAME ./dftd3.dat
           REFERENCE_FUNCTIONAL revPBE
           CALCULATE_C9_TERM  T
           REFERENCE_C9_TERM  T
           LONG_RANGE_CORRECTION  F
         &END PAIR_POTENTIAL
       &END VDW_POTENTIAL
     &END XC

.....


     &KIND H
       BASIS_SET 6-31G*
       POTENTIAL ALL
       LEBEDEV_GRID  80
       RADIAL_GRID  200
     &END KIND
     &KIND O
       BASIS_SET 6-31G*
       POTENTIAL ALL
       LEBEDEV_GRID  80
       RADIAL_GRID  200
     &END KIND

Also if there is else I can do either remove the "spikes" fully from the 
electron density cube, that would be really helpful as well.

Best Regards,
Mayank Dodia

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